Field of the Invention
The present invention relates to a storage medium having an image processing program stored thereon and an image processing apparatus, and more specifically to a storage medium having stored thereon an image processing program for moving an object displayed on a display device based on an input direction, and an image processing apparatus usable for such an image processing program.
Description of the Background Art
Conventionally, games (image processing) in which an object displayed on a display device is moved forward, rearward, leftward and rightward in a virtual world in accordance with an input by a user to a cross switch, a stick or the like are commonly played. For example, Japanese Laid-Open Patent Publication No. 2002-263359 (hereinafter, referred to as “patent document 1”) discloses a video game apparatus for moving an object in response to an operation in an “upward”, “downward”, “leftward” or “rightward” direction made on an analog joystick or a cross switch. The video game apparatus disclosed in patent document 1 is operated as follows. When a non-player object of interest is locked, a player object is moved in a “direction of moving toward the non-player object of interest”, a “direction of moving away from the non-player object of interest”, a “leftward direction while keeping the distance from the non-player object of interest”, or a “rightward direction while keeping the distance from the non-player object of interest” in accordance with the operation in the “upward”, “downward”, “leftward” or “rightward” direction, respectively. When a non-player object of interest is not locked, player object is moved “forward”, “rearward”, “leftward” or “rightward” in accordance with the operation in the “upward”, “downward”, “leftward” or “rightward” direction, respectively.
According to the conventional art, it is common that an object is moved in the forward-rearward direction in the virtual world when the operation is made in the upward-downward direction as described above. The reason is that the object is assumed to be moved on a plane which is set in the virtual world and that in an image represented in a display screen, the direction corresponding to the upward-downward direction intuitively perceivable by the player basically matches the forward-rearward direction in the virtual world. Therefore, it is not considered to move the object on a terrain with many unexpectable elements such that the standing direction of the object is changed in accordance with the position of the object (for example, the normal direction with respect to the direction of gravity or topography which is set in the virtual world is changed). In addition, when the topography of the position where the object is moving is significantly changed or when the direction of the virtual camera is rapidly changed, it is expected that the player loses the sense of the relationship between the moving direction of the object and the operation direction. As a result, it is expected that after the topography or the direction of the virtual camera is changed, the operation direction cannot be controlled to keep the moving direction continuous from before the change, and thus the operation becomes unstable.